JSFiddle - React, Tailwind, and code Playground

HTML

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Untitled Document</title>


</head>

<body>

<textarea id="textarea1"></textarea>
<br><input type="button" value="Write blah blah" onclick="addtxt('textarea1')">

</body>
</html>

JavaScript

function addtxt(input) {
 var obj=document.getElementById(input);
 obj.value+="blah test 123"
 }